Brake system including anti-lock control and electronic brake force distribution

ABSTRACT

A brake system including electronic anti-lock control (ABS) and electronically controlled brake force distribution (EBV). This brake system has electrically operable hydraulic valves, of which the inlet valves are open in their inactive position. An electronic error monitoring device is provided which responds upon the occurrence of defects or malfunctions and disconnects the control at least in part. The brake system also has control electronics including secondary circuits which remain in function after the error monitoring device has responded, and by which the inlet valves leading to the rear-wheel brakes are actuated and which are provided such that the pressure in the rear-wheel brakes is maintained constant when a limit value of the braking pressure in the master cylinder is exceeded.

This application is the U.S. national-phase application of PCTInternational Application No. PCT/EP93/03335.

BACKGROUND OF THE INVENTION

The present invention relates to a brake system including electronicanti-lock control (ABS) and electronically controlled brake forcedistribution (EBV) by means of electrically operated hydraulic valves,of which the inlet valves (i.e. the valves controlling the pressurefluid flow to the individual wheel brakes) are open in their inactiveposition. This brake system further includes control electronics togenerate the valve control signals in response to wheel sensor signalsrepresentative of the rotational behavior of the individual wheels, andan error monitoring device which responds upon the occurrence of defectsor malfunctions and disconnects or deactivates the control at least inpart.

In up-to-date conventional brake systems including anti-lock control,the braking pressure is controlled by electrically orelectromagnetically controllable inlet and outlet valves. The inletvalves are arranged in the pressure fluid conduit from the mastercylinder to the wheel brakes. The pressure fluid conduits, in which theoutlet valves are arranged, lead from the wheel brakes to a supplyreservoir or a pressure fluid return pump. To ensure the uncontrolledbrake function when the control system is deactivated or the currentsupply is disconnected, the inlet valves are provided as SO-valves (i.e.open in their de-energized condition), and the outlet valves areprovided as SG-valves (i.e. closed in their de-energized condition). Toreliably prevent dangerous overbraking of the rear wheels in anysituation, even upon deactivation of the control, conventional pressurereducing valves or so-called brake force regulators are inserted intothe pressure fluid conduits leading to the rear wheels in suchslip-controlled systems.

Further, it is known to bypass these brake force regulators during ananti-lock control operation for introducing a particularly high amountof braking pressure into the rear-wheel brakes during a controloperation in case of need. Upon failure of the anti-lock controller, thebrake force regulators will operate to full effect.

Still further, it is known from German DE-A 33 23 402 to utilize theelectrically operable hydraulic valves, which are required for ananti-lock control operation, also to control the brake forcedistribution to the front axle and rear axle which is necessary as aresult of dynamic axle load shifts. In this publication, the inletvalves in the lines leading to the rear wheels take the form ofSG-valves. These valves effect introduction of the pressure into thewheel brakes of the rear wheels in a decelerated fashion, so that therearwheel slip maximally adopts a predetermined percentage of the slipwhich occurs on the front wheels. The pressure fluid conduit leading tothe rear wheels is permanently closed in such a brake system upondeactivation of the electronic control.

Attempts have been made, for cost reasons, to use anti-lock brakesystems in which additional brake force regulators are avoided. Anelectronic control or regulation of brake force distribution by means ofanti-lock control valves, in particular inlet valves, is desirable. Uponmalfunction or deactivation of the controller due to a defect, however,braking pressure introduction, even into the rear-wheel brakes, shouldbe possible now as before. Thus, it is inappropriate that the valve inthe conduit leading to the rear wheels is a SG-valve.

SUMMARY OF THE INVENTION

An object of the present invention is to develop a brake system withanti-lock control and electronic brake force distribution which permitsbraking pressure delivery to the rear-wheel brakes even if thecontroller is deactivated due to malfunction, and, additionally,overbraking of the rear wheels is prevented which is linked to the riskof skidding, as is known.

It has been discovered that this object can be achieved by a brakesystem of the previously mentioned type, the special features residingin the fact that the control electronics include secondary circuitswhich remain operative after response of the error monitoring device, byway of which the inlet valve leading to the rear-wheel brakes iscontrollable, and which are provided such that the pressure in therear-wheel brakes is maintained constant or limited in dependence on thebraking pressure in the master cylinder, or when a predeterminedpressure threshold is exceeded, or in dependence on a measured quantityrelated to vehicle dynamics, such as vehicle deceleration, or the like.

Thus, according to the present invention, braking pressure is introducedinto the rear-wheel brakes on operation of the brake, even if thecontroller is deactivated by the error monitoring device, until apressure level is reached in the master cylinder which gives rise tofear overbraking of the rear-wheels. Starting from this moment, thebraking pressure in the rear-wheel brakes is maintained constant.

According to a favorable embodiment of the present invention, thehydraulic valves, with the exception of the inlet valves leading to therear-wheel brakes, are connected to the voltage supply by way of amechanical or electronic disconnecting relay which is controlled by theerror monitoring device and, on detection of malfunction, interrupts thevoltage supply of the hydraulic valves, with the exception of therear-wheel inlet valves. This relay is a real "disconnecting" relay; notthat there is the need for "switch over" to another potential or toground. This is of vital importance for safety reasons.

According to another aspect of the present invention, the secondarycircuit includes a driver to actuate the inlet valves leading to therear-wheel brakes. The driver is actuated by the control electronics byway of a logic circuit only if the current supply of the other hydraulicvalves is disconnected and a pressure switch, operated by the hydraulicpressure in the master cylinder, or a switch responding to the vehicleacceleration has reacted.

Further, according to a favorable aspect of the present invention, testpulses are fed, in a manner known per se, to the secondary circuit byway of the controller electronics, and the reactions to these testpulses are monitored for plausibility.

According to still another development of the present invention, aplurality of inlet valves leading to the rear-wheel brakes areactuatable by a joint secondary circuit, the inlet valves beingconnected to a joint end stage or, respectively, the driver of thesecondary circuit by way of decoupling diodes.

Also, according to the present invention, the pressure-responsive oracceleration-responsive switches serve to acquire additional informationfor the control as long as the error monitoring device does not respond.

Further features, advantages and possible applications of the presentinvention can be seen in the following description with reference to theaccompanying drawings of embodiments of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a block diagram of the most important component parts of thecontrol electronics of a brake system according to the presentinvention, and

FIG. 2 is a block diagram of an alternative arrangement of the controlelectronics of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

For the sake of greater ease of understanding the present invention,only those components in FIG. 1 are represented symbolically which areimportant to the invention.

According to FIG. 1, control electronics 1 include a computer ormicroprocessor 2 permitting, in a known manner, generation of thesignals to control the braking pressure control valves (i.e. the inletand outlet valves) and to monitor and regularly check the system foroperability. FIG. 1 shows the winding of three control valves 3, 4, 5.Reference numeral 3 represents one of the inlet valves leading to therear-wheel brakes and, additionally, serving to control the brake forcedistribution. The other inlet and outlet valves have been assignedreference numerals 4, 5. Generally, one pair of inlet and outlet valvesis required for each wheel. Further, an end stage or driver 6, in theform of a power transistor, is shown which switches the valve 3 on andoff. All valves are connected to the supply voltage (i.e. the batteryvoltage U_(B) of the vehicle). Valve 3 is connected directly, whilevalves 4, 5 are connected by way of an electronic relay 7.

The secondary circuit, essential for the present invention, includes anend stage or a driver 8 similar to the driver 6. The control of inletvalve 3 can be switched on by this driver 8. Further, the secondarycircuit includes a logic circuit 9 having an output A at which thesignal to actuate the driver 8 is developed.

The secondary circuit is controlled, by way of the logic circuit 9, bythe microprocessor 2, the output AP of which is connected to the logiccircuit 9.

A signal to operate the driver 8 and, thus, to activate the winding ofthe inlet valve 3 is applied to the output A of the logic circuit onlyif an ignition switch 10 is closed and if it is signalled to the circuit9, through a signal line 11, that the electronic relay 7 has respondedand prevents current flow from the battery connection U_(B) to thecontrol valves 4, 5. Further, a pressure switch 12 is required to beclosed to drive the driver 8. Switch 12, which is open in its inactiveposition, reacts to the braking pressure P_(HZ) in the master cylinderof the brake system and closes as soon as the pressure P_(HZ) hasexceeded a predetermined limit value.

The control signal for the electronic relay 7 is furnished by an errormonitoring device 13. With the control electronics functioning properly(and the ignition switched on), the electronic relay 7 is open forcurrent supply.

The control electronics of the brake system according to the presentinvention shown in FIG. 1 operates as follows:

In the "normal case" (i.e. in the absence of a defect or malfunction,and outside the monitoring cycles), the electronic relay 7 is in theclosed condition so that the control valves 4, 5 are connected to thevoltage supply U_(B). The inlet valve 3 is permanently connected to thebattery.

According to a predetermined pattern and at predetermined times, forexample, after each closing of the ignition switch 10, a test cycle isinitiated by the output AP of the microprocessor 2. Whethercorresponding reactions and potential shifts occur are checked by ways,which are not illustrated in detail. A check by a number of plausibilitycriteria is possible in a known fashion which, therefore, does notrequire detailed explanation.

Whenever the control electronics 1 detect a defect or malfunction, theanti-lock control is deactivated for safety reasons. Deactivation iscarried out by "opening" the electronic relay 7 by a correspondingsignal issued by the error monitoring device 13. The control valves 4, 5become deenergized as a result. Only the inlet valve 3 leading to therear-wheel brakes continues to be connected to the voltage supply U_(B).If, on brake application, a predetermined limit value of the brakingpressure P_(HZ) in the master cylinder is exceeded, pressure switch 12responds. Because the ignition switch 10 is closed and the electronicrelay 7 became high-ohmic, all conditions in the logic circuit 9 aresatisfied to generate an output signal at output A which causesactuation of the driver 8 and, thus, of the SO-inlet valve 3. Inletvalve 3 closes and prevents further pressure increase in the rear-wheelbrakes. Overbraking of the rear wheels is avoided and, thus, the drivingstability of the vehicle is not jeopardized.

Further, a driver 14 is shown in FIG. 1 which is also actuated by themicroprocessor 2 and serves to switch on an alarm lamp 15 upon theoccurrence of defects. A switch 16 is shown in addition which can alsoswitch on the alarm lamp 15, for example, initiated by a too low brakefluid level in the supply reservoir of the brake system. Of course,there are generally still further functions which are monitored and, ina case of malfunction, initiate an alarm and/or switch-on of the lamp15.

FIG. 2 differs from the embodiment according to FIG. 1 only by theprovision and monitoring of two inlet valves 3, 3' which lead to therear-wheel brakes. By way of two decoupling diodes 17, 18, both inletvalves 3, 3' are connected to a joint driver 8'. Both inlet valves 3, 3'are connected to the battery voltage U_(B) directly, bypassing theelectronic relay 7'. In case of a malfunction, both inlet valves 3, 3'are actuated as soon as the pressure P_(HZ) in the master cylinder hasexceeded the predetermined limit value and the pressure switch 12' isclosed as a result.

Instead of, or in addition to, the pressure-responsive switch 12, 12'illustrated in FIGS. 1 and 2, an acceleration-responsive switch can beinstalled which responds to actuate the driver 8, 8', by way of thelogic circuit 9, as soon as the vehicle acceleration exceeds apredetermined limit value. Other measured quantities related to vehicledynamics may also serve to initiate actuation of the driver.

In addition, it is easily possible to use the pressure-responsive oracceleration-responsive switch 12, 12' not only for error monitoring butalso for improving the control. Depending on the type of switch orsensor, the information obtained by this switch or sensor can also beassessed for calculating the brake temperature, the braking pressure,the vehicle deceleration, etc. The microprocessor 2 can also be used tothis end.

Illustrated in dashed lines in FIG. 2 is a signal line 19 which leadsfrom the switch or sensor 12' directly to the microprocessor 2 andserves to evaluate the information furnished by the switch outside theerror monitoring device.

We claim:
 1. A brake control system for a vehicle having front wheelsand rear wheels, said brake system comprising:a plurality of controlvalves for controlling pressure fluid at brakes associated with thefront and rear wheels of the vehicle, including at least one rear-wheelbrake inlet valve for controlling pressure fluid flow to a firstrear-wheel brake associated with a first rear wheel of the vehicle and asecond rear-wheel brake associated with a second rear wheel of thevehicle; a switch responsive to at least one of:(a) braking pressurewhen a predetermined pressure threshold in a master cylinder in thevehicle is exceeded, and (b) a measured quantity related to vehicledynamics; control electronics responsive to wheel sensor signalsrepresentative of the rotational behavior of the wheels of thevehiclefor generating valve control signals for controlling each of theplurality of control valves; error monitoring means for detecting theoccurrence of defects and malfunctions in said control electronics andfor deactivating selected ones of said plurality of control valves otherthan said rear-wheel brake inlet valve; and a secondary circuit, whichremains operative after defects and malfunctions in said controlelectronics are detected, for controlling said rear-wheel brake inletvalve to maintain pressure in the first and second rear-wheel brakes ata limited level in response to said switch and to deactivation, by saiderror monitoring means, of selected ones of said plurality of controlvalves.
 2. A brake control system according to claim 1 wherein saidsecondary circuit controls said rear-wheel brake inlet valve to maintainthe pressure in the first and second rear-wheel brakes constant.
 3. Abrake control system according to claim 1 further including:a voltagesupply; and a relay, disposed between said-voltage supply and selectedones of said plurality of control valves other than said rear-wheelbrake inlet valve, for:(a) connecting said selected ones of saidplurality of control valves to said voltage supply, and (b)disconnecting, in response to said error monitoring means, said selectedones of said plurality of control valves from said voltage supply ondetection of a malfunction.
 4. A brake control system according to claim3 wherein said secondary circuit includes:a logic circuit responsive tosaid relay and'said switch for developing a control signal when saidrelay has disconnected said selected ones of said plurality of controlvalves from said voltage supply and the hydraulic pressure in the mastercylinder exceeds the predetermined pressure threshold, and a driver,responsive to said control signal developed by said logic circuit, foractuating said rear-wheel brake inlet valve.
 5. A brake control systemaccording to claim 4 further including means, responsive to said switchin the absence of a malfunction, for developing additional informationabout conditions of the vehicle.
 6. A brake control system according toclaim 3 wherein said secondary circuit includes:a logic circuitresponsive to said relay and said switch for developing a control signalwhen said relay has disconnected said selected ones of said plurality ofcontrol valves from said voltage supply and the acceleration of thevehicle exceeds a predetermined level, and a driver, responsive to saidcontrol signal developed by said logic circuit, for actuating saidrear-wheel brake inlet valve.
 7. A brake control system according toclaim 6 further including means, responsive to: said switch in theabsence of a malfunction, for developing additional information aboutconditions of the vehicle.
 8. A brake control system according to claim3 wherein said control electronics further include:means for:(a)supplying test pulses to said secondary circuit, and (b) monitoringreactions to the test pulses to determine plausibility.
 9. A brakesystems according to claim 1 wherein said rear-wheel brake inlet valvecontrols pressure fluid flow to only the first rear-wheel brake and saidbrake system further includes a second rear-wheel brake inlet valve forcontrolling pressure fluid flow to the second rear-wheel brake.
 10. Abrake system according to claim 9 wherein said secondary circuitcontrols sad rear-wheel brake inlet valves to maintain the pressure inthe first and second rear-wheel brakes constant.
 11. A brake systemaccording to claim 10 further including:a first rear-wheel brake outletvalve for controlling pressure fluid flow from the first rear-wheelbrake; a second rear-wheel brake outlet valve for controlling pressurefluid flow from the second rear-wheel brake; a voltage supply; and arelay, disposed between said voltage supply and said first and secondoutlet valves, for:(a) connecting said first and second outlet valves tosaid voltage supply, and (b) disconnecting, in response to said errormonitoring means, said first and second outlet valves from said voltagesupply on detection of a malfunction.
 12. A brake system according toclaim 11 wherein said secondary circuit includes:a pressure switchresponsive to hydraulic pressure in a master cylinder of the vehicle, alogic circuit responsive to said relay and said pressure switch fordeveloping a control signal when said relay has disconnected said firstand second outlet valves from said voltage supply and the hydraulicpressure in the master cylinder exceeds a predetermined level, and adriver, responsive to said control signal developed by said logiccircuit, for actuating said rear-wheel brake inlet valves.
 13. A brakesystem according to claim 12 wherein said secondary circuit furtherincludes:(a) a first decouple diode disposed between one of saidrear-wheel inlet valves and said driver, and (b) a second decouple diodedisposed between the other of said rear-wheel inlet valves and saiddriver.
 14. A brake system according to claim 13 wherein said controlelectronics further include:means for:(a) supplying test pulses to saidsecondary circuit, and (b) monitoring reactions to the test pulses todetermine plausibility.
 15. A brake system according to claim 13 furtherincluding means, responsive to said pressure switch in the absence of amalfunction, for developing additional information about conditions ofthe vehicle.
 16. A brake system according to claim 11 wherein saidsecondary circuit includes:a mechanical switch responsive toacceleration of the vehicle, a logic circuit responsive to said relayand said mechanical switch for developing a control signal when saidrelay has disconnected said first and second outlet valves from saidvoltage supply and the acceleration of the vehicle exceeds apredetermined level, and a driver, responsive to said control signaldeveloped by said logic circuit, for actuating said rear-wheel brakeinlet valves.
 17. A brake system according to claim 16 wherein saidsecondary circuit further includes:(a) a first decoupling diode disposedbetween one of said rear-wheel inlet valves and said driver, and (b) asecond decoupling diode disposed between the other of said rear-wheelinlet valves and said driver.
 18. A brake system according to claim 17wherein said control electronics further include:means for:(a) supplyingtest pulses to said secondary circuit, and (b) monitoring reactions tothe test pulses to determine plausibility.
 19. A brake system accordingto claim 17 further including means, responsive to said mechanicalswitch in the absence of a malfunction, for developing additionalinformation about conditions of the vehicle.
 20. A brake systemincluding:electronic anti-lock control (ABS) and electronicallycontrolled brake force distribution (EBV) by means of electricallyoperated hydraulic valves of which the inlet valves controlling thepressure fluid flow to individual wheel brakes are open in theirinactive position, control electronics to generate valve control signalsin response to wheel sensor signals representative of the rotationalbehavior of the individual wheels, and an error monitoring device whichresponds upon the occurrence of defects or malfunctions and disconnectsor deactivates the control at least in part, characterized in that:(a)the brake system further includes:(1) voltage supply, (2) a logiccircuit, (3) a pressure switch responsive to hydraulic pressure in themaster cylinder, and (4) a switch responsive to vehicle acceleration;(b) the control electronics include secondary circuits which:(1) remainoperative after response of the error monitoring device for controllingthe inlet valve leading to the rear-wheel brakes, and (2) are providedsuch that the pressure in the rear-wheel brakes is maintained constantor limited in dependence on at least one of:(i) the braking pressure,(ii) when a predetermined pressure threshold in the master cylinder isexceeded, and (iii) a measured quantity related to vehicle dynamics, (3)include a driver for actuating the inlet valves leading to therear-wheel brakes, the driver being actuated by the control electronicsby way of the logic circuit only if the voltage supply is disconnectedfrom the other hydraulic valves and the pressure switch, operated by thehydraulic pressure in the master cylinder, or a switch responding to thevehicle acceleration is operated; and (c) the hydraulic valves, with theexception of the inlet valves leading to the rear-wheel brakes, areconnected to the voltage supply by way of a mechanic or electronicdisconnecting relay which is:(1) controlled by the error monitoringdevice, and (2) on detection of malfunction, interrupts the voltagesupply of the hydraulic valves.
 21. A brake system as claimed in claim20 characterized in that test pulses are fed to the secondary circuit bythe controller electronics, and the reactions to these test pulses aremonitored for plausibility.
 22. A brake system as claimed in claim 21,characterized in that a plurality of inlet valves leading to therear-wheel brakes are actuatable by a joint secondary circuit, the inletvalves being connected to a joint end stage of the secondary circuit byway of decoupling diodes.
 23. A brake system as claimed in claim 22,characterized in that the pressure-responsive or acceleration-responsiveswitches serve to acquire additional information for the control as longas the error monitoring device does not respond.